The handling of carcinogenic powders and toxic chemicals in paper bags has proven to be a hazardous and dangerous operation. Therefore, the Federal Government has regulated that such materials be used in a manner which precludes any operator being exposed to breathing or directly contacting such materials. Also, since many of these materials are very dense and of a nature that readily compacts during shipment, the use of rigid containers with conventional side door discharge or bottom cone discharge has not proven practical.
These discharge problems have resulted in the development and use of self-contained portable containers which have a fluid bed or porous floor which permits introducing air to fluidize the material within the container so that it will flow therefrom either by gravity or by means of a screw conveyor, a porous-floor conveyor, or a vacuum system. Such containers may be round, square, or rectangular and may have rigid sides or flexible sides which permit meeting of the containers when they are empty, but all have the porous floor or fluid bed concept as a common feature.
The fluid bed or porous floor concept requires that air be induced under the porous floor so that it will permeate through the porous floor and aerate the material and cause it to be fluidized. This requires that a vent system be applied to the porous floor container, no matter whether the container is being gravity discharged, discharged through a vacuum conveying system, a porous-floor conveyor, or by a screw conveyor, since the volume of fluidizing air introduced to the container must be released from the container. Such air passes through the material during aeration and consequently picks up fine particles of the material so that the air which must be released from the container includes large amounts of the solid particulate material, which may be carcinogenic or toxic, in the form of air-borne dust or powder. It is imperative that this contaminated air be contained so that is is not permitted to pollute the air in the work space around the container or the atmosphere if it is discharged outside the building.